Driving mode ride height adjustment

ABSTRACT

Apparatus for adjusting the height of a vehicle frame on a vehicle is disclosed including a pneumatic suspension system for adjusting the elevation of the vehicle frame, and a controller for controlling the pneumatic suspension system, the controller being adapted to be set in a first mode corresponding to normal driving of the vehicle and a second mode corresponding to parking or marshalling of the vehicle, whereby when the controller is in the first mode, the pneumatic suspension system permits adjustment of the vehicle frame within a first range and when the controller is in the second mode the pneumatic suspension system permits adjustment of the vehicle frame within the second range, the first range being greater than the second range, and the second range being within the first range.

FIELD OF THE INVENTION

The present invention relates to an apparatus for adjusting the drivingmode ride height of a vehicle having a pneumatic suspension system.

BACKGROUND OF THE INVENTION

When load-carrying vehicles (LCV's) are to be loaded and unloaded, theyare normally brought to a loading dock. In order to facilitate and toincrease the efficiency of such loading and unloading, the height of theloading dock should be adapted to the elevation of the loading platformof the LCV. One way of achieving this result is to construct a loadingdock having a variable elevation. Such an approach may be economicallyfeasible with highly utilized loading docks, such as goods terminals,where loading and unloading are very frequent.

Another method of solving the problem of adapting the height of theloading dock and the elevation of the LCV loading platform is to controlthe elevation of the vehicle loading platform. Such an approach has theadvantage of allowing for adaptation to loading docks having a fixedheight.

Such a system is described, for example, in British Patent No.2,237,780.

This patent describes a system in which the LCV loading platform islocated at a predetermined height when the vehicle is operated in itsnormal driving mode. When the vehicle is parked for loading andunloading, however, the elevation of the LCV loading platform isadjustable so as to allow for adaptation of its elevation to the heightof the loading dock, thus enabling efficient loading and unloading. Whenthe LCV is to once again be operated in a normal driving mode, theoriginal fixed elevation of the LCV loading platform is restored.

PCT Application No. WO 91/07291 discloses another apparatus of the typedisclosed above.

One problem exhibited by the prior art is that the height assumed by theLCV loading platform, when restoring the elevation of the LCV loadingplatform for normal operation of the LCV, after performing heightadjustment during loading and unloading, is fixed and cannot be varied.Therefore, when the vehicle is operated in a normal driving mode, i.e.when the vehicle is not parked or is driven at a speed exceeding arelatively low speed, the elevation of the LCV loading platform in mostcases cannot be adjusted, and in those cases where the elevation isadjustable, it is adjustable within the same range as the permittedrange for loading and unloading. This initially means that controlpossibilities are not available, which is a disadvantage with this typeof prior art, and secondly that the ride height in the driving mode isadjustable within a range where a risk of damage to the load and the LCVexists.

It has been determined by tests and calculations that the aerodynamicproperties of an LCV are dependent on the elevation of the LCV loadingplatform. Such tests and calculations have shown that is preferable, forobtaining an LCV having a lower air resistance, and thus a lower fuelconsumption, for the elevation of the LCV loading platform to be as lowas possible when the vehicle is operated in a driving mode.

Thus, it is an object of the present invention, by providing the LCVwith a possibility of adjusting the elevation of the LCV loadingplatform, to permit the vehicle to be operated in the driving mode witha low set driving mode elevation or ride height, thereby reducing boththe air resistance and the fuel consumption.

A second advantage of being able to lower the elevation of the LCVloading platform is, in those cases where the absolute height of the LCVis limited by regulations or accessibility, that a larger loading heightcan be utilized, thereby improving the financial strength of the LCV.

Thus, another object of the present invention is, by providing the LCVwith a mechanism to control the height of the loading platform, toensure that the LCV can be driven with a low ride height, whereas theLCV can carry further load, which improves the economy for the LCV.

A further advantage of being able to lower the ride height of the LCVframework is that this lowers the cab instep height which increasesdriver comfort.

Thus, it is another object of the present invention, by providing theLCV with the ability of adjusting the ride height of the LCV framework,and thereby that of its loading platform and cab, which are affixed tothe framework, to lower the cab instep height thereby increasing drivercomfort.

An LCV loading platform is resiliently suspended by the structurecarrying wheel axles and wheels. Thus, when the LCV is operated in thedriving mode, the LCV loading platform will oscillate around the heightlevel that the loading platform has assumed in an equilibrium position,when standing still. The amplitude of loading platform oscillationsaround its equilibrium position is dependent of the quality of the road,the load weight, the vehicle speed, and the characteristics of theloading platform suspension.

As discussed above, the loading platform of an LCV is fitted to thewheel-carrying structure by resilient means. Such resilient meansdisplay elastic properties within a certain range of expansion andcompression. If the resilient means are compressed excessively, theywill then act like a rigid connection. Such excessive compression willoccur if the loading platform has been adjusted to an excessively lowposition when the LCV is operated in a driving mode. This means that theharmonic oscillation which, when the loading platform elevation iscorrectly adjusted, occurs around the equilibrium position of theloading surface height level, is replaced by an interrupted oscillationwhen the resilient means is compressed past its elastic range. Wheninterrupted oscillatory motions take place, large accelerations occur,leading to the load, the resilient means, and the LCV as a whole, beingsubjected to very high stress forces. If the loading platform isadjusted to an excessively high position, problems will also occur, inthat the resilient means may be extended in excess of the elastic range.In such cases, an interrupted oscillatory motion also occurs leading tohigh stress forces on the load, the resilient means, and on the LCV as awhole.

Yet another object of the present invention is to provide the LCV with ameans of adjusting the elevation of its loading platform, thus allowingfor adjustment within a first, larger range when the vehicle has takenup a parking or marshalling position, and adjustment within a second,smaller range when the vehicle has taken up a driving mode. Adjustmentof the ride height will thus be allowed when the vehicle is in a drivingmode, but the elevation or ride height in this mode can only be adjustedwithin a range which is not detrimental to either the load or thevehicle.

One advantage of allowing the ride height of the vehicle framework andloading platform to be adjusted to as high a level as possible is thatthe framework ground clearance increases. This is of importance when thevehicle is driven over bad ground and when the vehicle is driven acrossangled ramps and steep structures.

Still another object of the present invention is, by providing the LCVwith a means of adjusting the elevation of the vehicle framework andloading platform, that the driver will be able to selectively adjust theride height in accordance with various conditions. Thus, if the vehicleis to be driven on a flat road as low a ride height as possible is ofinterest, or if the vehicle is driven over bad ground or across steepramps and structures, as high a ride height as possible is of interest.

A still further advantage of having the vehicle framework and loadingplatform adjustable within a first, larger range when the vehicle hastaken up a parking or marshalling position and a second smaller rangewhen the vehicle has taken up a driving mode is that the vehicle cardanshaft, which is provided for connecting an output shaft of atransmission arranged in the vehicle to a driving wheel axle, isconnected to the driving wheel axle in a certain angular position. Whenthe vehicle is standing still or being driven at low speed, a relativelylarge deviation from this position is allowable. When the vehicle isdriven at a higher speed, only a smaller deviation from this angularposition is allowable. As the cardan shaft is carried by the samestructure that carries the vehicle loading platform, that is the vehicleframework or frame structure, the elevation of the framework, the framestructure, or the loading platform, must only be adjustable within asmaller range when in the driving mode.

It is also an object of the present invention by providing the LCV witha means of adjusting the elevation of its loading platform, thusallowing adjustment within a first, larger range when the vehicle hastaken up a parking or marshalling position, and within a second smallerrange when the vehicle has taken up a driving mode to allow adjustmentof the ride height when the vehicle is in the driving mode, at the sametime allowing the ride height only to be adjusted within a range that isnot detrimental to the cardan shaft and its suspension.

SUMMARY OF THE INVENTION

In accordance with the present invention, these and other objects havenow been realized by the invention of apparatus for adjusting the heightof a vehicle frame on a vehicle including a vehicle suspension system,the apparatus comprising vehicle frame elevation adjustment means foradjusting the elevation of the vehicle frame, and control means forcontrolling the vehicle frame elevation adjustment means, the controlmeans adapted to be set in a first mode corresponding to normal drivingof the vehicle and a second mode corresponding to parking or marshallingof the vehicle, whereby when the control means is in the first mode thevehicle frame elevation adjustment means permits adjustment of thevehicle frame within a first range and when the control means is in thesecond mode the vehicle frame elevation adjustment means permitsadjustment of the vehicle frame within a second range, the first rangebeing greater than the second range, and the second range being withinthe first range.

In a preferred embodiment, the vehicle frame elevation adjustment meanscomprises a pneumatic suspension system for the vehicle. Preferably, thevehicle includes at least one wheel axle, and the vehicle frameelevation adjustment means adjusts the elevation of the vehicle framewith respect to the at least one wheel axle.

In accordance with a preferred embodiment of the apparatus of thepresent invention, the pneumatic suspension system is arranged betweenthe vehicle frame and the at least one wheel axle, the control meansincluding selector means for selecting one of the first and secondmodes, and the pneumatic suspension system including a source ofcompressed air, valve means for selectively feeding the compressed airto the pneumatic suspension system or drawing the compressed air fromthe pneumatic suspension system in response to the control means,whereby the pneumatic suspension system is expanded or compressed inorder to adjust the distance between the vehicle frame and the at leastone wheel axle, the distance between the vehicle frame and the at leastone wheel axle being adjusted within the first range when the controlmeans is in the first mode and within the second range when the controlmeans is in the second mode. Preferably, the apparatus includesmeasuring means for measuring the distance between the vehicle frame andthe at least one wheel axle.

In accordance with one embodiment of the apparatus of the presentinvention, the measuring means comprises an angular position sensor, alever connected to the angular position sensor, and a control rodarticulated with respect to the lever, the angular position sensor beingattached to one of the vehicle frame and the at least one wheel axle andthe control rod being attached to the other of the vehicle frame and theat least one wheel axle, whereby the angular position sensor measuresthe angular position of the lever so that when the distance between thevehicle frame and the at least one wheel axle is altered by means of thepneumatic suspension system the position of the control rod is altered,thereby altering the angular position of the lever sensed by the angularposition sensor, the control means including means for reading theangular position of the lever and determining the distance between thevehicle frame and the at least one wheel axle based thereon.

In accordance with a preferred embodiment of the apparatus of thepresent invention, the pneumatic suspension system includes air bellowscomprising a flexible material, a base for the air bellows, and a topfor the air bellows, the air bellows, the base and the top defining aclosed space, and passage means connecting the valve means with theclosed space, the pneumatic suspension system including a cylindricalsurface, whereby the bellows is adapted to roll onto the cylindricalsurface when the pneumatic suspension system is compressed and to rolloff of the cylindrical surface when the pneumatic suspension system isextended. Preferably, the cylindrical surface is incorporated in thebase, and the base is attached to the at least one wheel axle. In apreferred embodiment, the cylindrical surface comprises a hollow body,whereby the volume of the closed space is increased.

In accordance with one embodiment of the apparatus of the presentinvention, the apparatus includes selector means connected to thecontrol means, the selector means being manually settable between thefirst mode and the second mode.

In accordance with another embodiment of the apparatus of the presentinvention, the apparatus includes vehicle speed detection means fordetecting the speed of the vehicle, whereby the control means is set inthe first mode when the speed of the vehicle is greater than apredetermined speed and the control means is set in the second mode whenthe speed of the vehicle is below the predetermined speed. Preferably,the predetermined speed is 0 km/hour, and in another embodiment thepredetermined speed is 20 km/hour.

In accordance with another embodiment of the apparatus of the presentinvention, the limits of the first range are defined by the maximumextension and compression of the pneumatic suspension system.

In accordance with another embodiment of the apparatus of the presentinvention, the vehicle includes a cardan shaft, and the limits of thesecond range are defined by the maximum and minimum angle of the cardanshaft and by a required upward and downward suspension stroke.

In accordance with the present invention, apparatus has also beenprovided for adjusting the distance between a vehicle frame and at leastone wheel axle of a vehicle having a suspension system, the apparatuscomprising a control unit including control members for setting adesired value for the distance, control means adapted to be set in afirst mode and a second mode, and selector means for selecting one ofthe first and second modes for the control means whereby when thecontrol means is in the first mode the desired value for the distance iswithin a first range and when the control means is in the second modethe desired value for the distance is within a second range, the firstrange being greater than the second range, and the second range beingwithin the first range. In a preferred embodiment, the vehicle includesa cab and wherein the control means is attachably mounted in the cab.

In accordance with one embodiment of the apparatus of the presentinvention, the first mode corresponds to normal driving of the vehicleand the second mode corresponds to parking or marshalling of thevehicle. In another embodiment, the selector means comprises a manualswitch.

In order to achieve the above objects of the present invention,apparatus is thus provided for adjustment of the driving mode elevationof a vehicle, where the vehicle elevation is adjustable within a second,smaller range when the control device has taken up its driving mode, thesecond smaller range lying within the first, larger range for theparking or marshalling mode.

In one embodiment of the present invention, pneumatic suspension meansarranged on the vehicle are utilized as the means changing the heightlevel of the vehicle for adjustment of the distance between the wheelaxle of the vehicle and the vehicle load-carrying structure, and therebythe elevation of the vehicle loading platform. According to theseembodiments, mounting of further height regulation means are avoidedwhich is space, weight and resource saving.

In one embodiment of the present invention, measuring means are used fordetermination of a measurement of the distance between the wheel axleand the load-carrying structure, which means that a more exact controlof the elevation of the frame structure and the loading platform can beachieved.

According to another embodiment of the present invention, a control unitis provided for adjustment of the distance between a load-carryingstructure and at least one wheel axle of a vehicle, where the distanceis adjustable within a first, larger range when an integral controldevice in the vehicle has taken up its parking or marshalling mode, andthe vehicle ride height is adjustable within a second, smaller rangewhen the control device has taken up its driving mode, the secondsmaller range lying within the first, larger range.

“Driving mode ride height” refers to the elevation of the loadingplatform when the LCV is operated in the driving mode.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be described in greater detail below withreference to the following detailed description, which in turn refers tothe drawings, in which:

FIG. 1 is a front, perspective, partially schematic view of an LCV;

FIG. 2 is a side, elevational, sectional view of a pneumatic suspensionmeans;

FIG. 3 is a side, perspective view of a measuring means for determiningthe distance between the wheel axle and the frame structure of avehicle;

FIG. 4 is a circuit diagram of the vehicle's pneumatic system;

FIG. 5a is a schematic representation of the LCV with the elevation ofthe loading platform set into an intermediate position;

FIG. 5b is a schematic representation of the LCV with the elevation ofthe loading platform set into one extreme end position;

FIG. 5c is a schematic representation of the LCV with the elevation ofthe loading platform set into the other extreme end position;

FIG. 6 is a schematic representation of the driving mode ride heightrange in relation to the parking and marshalling ride height range forthe LCV; and

FIG. 7 is a front, perspective view of a control unit for control andsetting of the distance between wheel axle and frame structure.

DETAILED DESCRIPTION

Turning to the drawings, in which like reference numerals refer to likeelements thereof, FIG. 1 shows, schematically, an LCV 1. The vehicleshown in the figure is a tractor vehicle. The invention may, however, beutilized on a tractor vehicle as well as on a trailer. The LCV 1 isconstructed around a frame structure 2 which is intended to carry thecab 3 of the LCV, as well as other vehicle apparatus, the LCV front axle(not shown) and the LCV rear axle 4. The frame structure is alsointended for supporting the load-carrying structure of the LCV.

According to the present invention, the load-carrying structure ispreferably comprised of a planar loading platform, as the presentinvention is particularly advantageous for use in connection withvehicles equipped with loading height level adjustment for thefacilitation of loading and unloading. It is possible, however, toutilize some other type of load-carrying structure, such as an upperbody, a container transportation device, or a tank body.

The frame structure is mainly comprised of two longitudinal girders, 5and 6, connected by a number of transversal girders, 7 and 8.

The front axle is suspended by a (not shown) wheel axle suspension.

The rear axle 4 is suspended by a wheel axle suspension 9.

The wheel axle suspension, which is of a conventional type, is comprisedof longitudinal stays, 10 a and 10 b, one on each side of the vehicle,which are affixed to the wheel axle 4, one transverse stay 11 thatconnects the two longitudinal stays, 10 a and 10 b, vertical V-shapedbrackets, 12 a and 12 b, connecting the longitudinal stays to the LCVframe structure, and diagonal stays, 13 and 14, connecting a centralportion of the wheel axis 4 to the frame structure 2. Thesestays/brackets ascertain that the wheel axle is fixed longitudinally andtransversally relative to the vehicle. However, the wheel axle ismovable around the pivot points, 15 a, 15 b, 16 a, and 16 b, aroundwhich an axle parallelogram is formed by the longitudinal stays, 10 aand 10 b, and the diagonal stays, 13 and 14. The suspension of the wheelaxle by these stays means that the wheel axle is movable along anarcuate path. In the area around the normal height level position of thewheel axle relative to the frame structure, the wheel axle movesprincipally in a plane perpendicular to the extension of the girders.

The vertical position of the wheel axle relative to the frame structurecan be adjusted by means of height adjustment means. The heightadjustment means consists of the pneumatic suspension, 17 a and 18 a, ofthe LCV. The pneumatic suspension will be described in greater detailbelow, in connection with FIG. 2.

Between the wheel axle 4 and the frame structure, distance measurementmeans 29 are arranged, measuring the distance between wheel axle andframe structure. The distance measurement means is described in greaterdetail below, in connection with FIG. 2.

The pneumatic suspension means, 17 a, 17 b, 18 a and 18 b, each comprisean air bellows 20, made of rubber. The air bellows defines a closedspace, together with a bottom structure 24 and a top structure 25affixed to the bellows. The top structure of the air bellows consists ofa bead plate 23, threaded onto the top end of the air bellows and fixedto a bellows plate 21. The bottom structure 24 exhibits a cylindricalsection 26. The air bellows is, except when it has attained its maximumextended position, partly rolled up onto the cylindrical section 26. Thebellows is arranged to be rolled off the cylindrical section when thepneumatic suspension means is extended, and to be rolled up onto thecylindrical section when the pneumatic suspension means is compressed.The bottom structure 24 comprises a hollow body, which is provided toincrease the total air content of the air bellows, thereby creating anair spring with enhanced spring characteristics.

Inside the air bellows there is provided a rubber spring cushion 27 forthe purpose of absorbing the load and impacts should the air springfunction deteriorate.

The total height of the air spring is controlled by filling the airbellows with, or draining the air bellows of, compressed air. For thispurpose, the pneumatic spring is provided with a connection 22 to apneumatic system arranged on the vehicle.

FIG. 3 shows a means 29 for measurement of the vehicle ride height, i.e.a height level sensor. This means comprises an angular position sensor30, a lever connected to the angular position sensor, and a control rod33 connected by a joint 32. The control rod 33 is in turn connected tothe wheel axle 4 by means of a joint 34. When the pneumatic suspensionis filled with or drained of compressed air, the elevation of the LCVframe structure is changed, pushing the control rod upwards ordownwards, which in turn changes the angular position of the lever 31.The angular position of the lever is sensed by the angular position 30,whereby the distance between wheel axle and frame structure, and therebythe elevation of the vehicle, can be determined.

FIG. 4 shows, as a circuit diagram, the function of an apparatus 39 foradjusting the elevation of the vehicle frame structure. The apparatussubstantially consists of a pneumatic system 40. An electronic controlunit 80, a control unit 90, and height level sensors, 81, 82 and 83, areconnected to the apparatus 39. The pneumatic system 40 controls theentry and exit of compressed air to the forward, 41 and 42, and therear, 43, 44, 45 and 46, air bellows. The pneumatic system comprises acompressed air storage means 47 consisting of a number of compressed airreservoirs. The compressed air storage means 47 is connected to a firstvalve means 48 by means of a supply line 49. The first valve meanscomprises a first solenoid valve 50, a second solenoid valve 51, and athird solenoid valve 52.

The second solenoid valve 51 exhibits a first port 53, a second port 54,and a third port 55, to which lines are connected. A drain line 56 isconnected to the first port 53. The drain line leads to the surroundingatmosphere through an air filter 57. The supply line 49 is connected tothe second port 54. A first connection line 58 is connected to the thirdport 55, connecting the second solenoid valve 51 to a main line 59.

The first solenoid valve 50 is operable between a first position 50 aand a second position 50 b.

The second solenoid valve 51 is operable between a first position 51 aand a second position 51 b.

The third solenoid valve 52 is operable between a first position 52 aand a second position 52 b.

When the second solenoid valve 51 is set to its first position 51 a, thesecond port 54 is connected to the third port 55 by an internal passagein the solenoid valve, whereby the main line 59 is connected to thesupply line 49 by means of the first connection line 58. This means thatcompressed air can be fed from the compressed air storage means 47 tothe main line 59. The first port of the second solenoid valve 51 isblocked when the solenoid valve is in this position, and therefore nocompressed air is drained to the surrounding atmosphere.

When the second solenoid valve 51 is set to its second position 51 b,the third port 55 is connected to the first port 53 by an internalpassage in the solenoid valve, whereby the main line 59 is connected tothe drain line 56. This means that compressed air from the main line 59is released to the surrounding atmosphere through the drain line 56. Thesecond port 54 of the second solenoid valve is blocked when the solenoidvalve is in this position, and therefore no compressed air is allowed toenter the main line from the compressed air storage means 47.

The first solenoid valve 50 and the third solenoid valve 52 areconnected to the main line 59 by a second connection line 60 and a thirdconnection line 61. The first and the third solenoid valves are bothdesigned with two ports, 62, 63, 64 and 65.

When the first solenoid valve 50 is set to its first position 50 a, thefirst port of the first solenoid valve is connected to its second portby an internal passage, whereby an inlet line 66 is connected to themain line 59. Compressed air can then be fed from the main line to theinlet line, by means of an inlet, to the bellows, 43 and 44, if a higherpressure exists in the main line than in the bellows, 43 and 44, whichis the case when the main line is in connection with the compressed airstorage means 47. If the pressure in the main line is lower than in thebellows, 43 and 44, which is the case when the main line is inconnection with the drain line 56, compressed air is transported fromthe bellows to the main line.

When the first solenoid valve 50 is set to its second position 50 b, thefirst and the second ports of the first valve are blocked, whereby thebellows associated with the first valve are pneumatically isolated fromthe surroundings. This means that when the first valve is set to thisposition, compressed air can neither be fed into nor be drained out fromthe bellows.

When the third solenoid valve 52 is set to its first position 52 a, thefirst port of the third solenoid valve is connected to its second portby an internal passage, whereby an inlet fine 67 is connected to themain line 59. Compressed air can then be fed from the main line to theinlet line, through an inlet to the bellows, 45 and 46, associated withthe third solenoid valve, if a higher pressure exists in the main linethan in the bellows, 45 and 46, which is the case when the main line isin connection with the compressed air storage means 47. If the pressurein the main line is lower than in the bellows, 45 and 46, which is thecase when the main line is in connection with the drain line 56,compressed air is transported from the bellows to the main line.

When the third solenoid valve 52 is set to its second position 52 b, thefirst and the second ports of the third valve are blocked, whereby thebellows associated with the third valve are pneumatically isolated fromthe surroundings. This means that when the third valve is set to thisposition, compressed air can neither be fed into nor be drained out fromthe bellows.

The main line 59 is provided besides the connections to the firstsolenoid valve and the second solenoid valve with a connection to asecond valve means 68. The second valve means 68 controls the flow intoand out from the forward air bellows, 41 and 42. The forward valve meansmay be arranged so as to allow separate supply to the left hand andright hand bellows. In that case, a set of at least two solenoid valvesis needed. As the loading of the front axle is substantiallysymmetrical, it is sufficient for the valve means to allow simultaneousand identical compressed air supply to the forward bellows in theembodiment shown in FIG. 4. The second valve means consists of a fourthsolenoid valve 69. The fourth solenoid valve comprises a first port 70,a second port 71, and a third port 72. The fourth solenoid valve isoperable between a first position 71 a, and a second position 71 b.

When the fourth valve is set to its second position 71 b, the secondport 71 is connected to the third port 72 by an internal passage in thesolenoid valve, which is provided with a restrictor 73. When thesolenoid valve is set to this position, the two forward bellows, 41 and42, communicate with each other by means of inlet lines, 74 and 75, andthe internal passage in the fourth solenoid valve. The first port 70 ofthe fourth solenoid valve is blocked in this position, allowingcompressed air neither to be fed into or to be drained out from thebellows.

When the fourth valve is set to its first position 71 a, the first port70 is connected to the second and third ports, 71 and 72, throughinternal passages 76 in the solenoid valve. When the solenoid valve isset to this position, the two forward bellows, 41 and 42, communicatewith the main line 59 by means of inlet lines, 74 and 75, and theinternal passages 76 in the solenoid valve. The first port of the fourthvalve is open in this position, whereby air can flow into or out fromthe bellows in dependence of the setting of the first valve means 48.

The solenoid valves comprised in the first and second valve means areoperable into their respective first and second positions by means ofsignals from a control device 80. The solenoid valves assume, in theirnon-actuated mode where no current is flowing through a solenoidarranged in each solenoid valve, their respective second positions. Thesolenoids are biased to this position by a mechanical spring included ineach solenoid valve, which holds the solenoid valve in its secondposition. When a current flows through the solenoid arranged in eachsolenoid valve, a magnet core provided inside the solenoid compressesthe mechanical spring, whereupon the solenoid valve assumes its firstposition.

Height level sensors, 81, 82 and 83, are connected to the control device80, supplying said means with information about the position of each airbellows. Thereby, the elevation of the LCV may be determined. Thecontrol device then controls the position of each of the valve means, orsolenoid valves, so as to set and maintain, respectively, the desiredelevation of the vehicle. The control device comprises memory cellswhere limit values for a larger range, 20 a and 20 b, and a smallerrange, 21 a and 21 b, are stored. Furthermore, a factory set defaultposition 20 c is also stored. The factory set position can be resumed bysetting the control unit to a default position. The size of the largerrange is determined in the case of the present invention being utilizedfor a vehicle having a pneumatic suspension substantially by the maximumstroke of the air bellows. The size of the smaller range is determinedby that range within which the elevation can be maintained withoutcausing damage to the vehicle when operated in the driving mode.

The number of devices for adjusting the loading platform elevation ispreferably three. In the case of three elevation adjustment devicesbeing used, they are preferably arranged in such a manner that onedevice controls the front end of the LCV, one controls the LCV rear leftsection, and one controls the LCV rear right section. In this manner, alevel control can be achieved in such a way that the loading platformremains in a horizontal plane, even if the LCV is loaded with a loadweighing more heavily on one side of the LCV.

FIGS. 5a to 5 c show the LCV seen from behind, with the device foradjustment of the loading platform elevation set to one intermediateposition and two extreme end positions. In FIG. 5a, the loading platform2 assumes an intermediate position, from which it may be raised as wellas lowered. In FIG. 5b, the device for adjustment of the loadingplatform elevation has been set for the loading platform to assume itsabsolutely lowest position. In this position there is no possibility ofdownwards resiliency by compression of the elevation adjustment device.This means that such an extreme position cannot be utilized when the LCVis in the driving mode, as the loading platform in this case is onlyresiliently suspended for movement towards a higher elevation of theloading platform. In FIG. 5c, the device for adjustment of the loadingplatform elevation has been set for the loading platform to assume itsabsolutely highest position. In this position there is no possibility ofupwards resiliency by extension of the elevation adjustment device. Thismeans that such an extreme position cannot be utilized when the LCV isin the driving mode, as the loading platform in this case is onlyresiliently suspended for movement towards a lower elevation of theloading platform.

The ride height 100 designates the distance from the load-carrying framestructure to the ground level 101.

FIG. 6 shows an example of within what ranges the elevation may beadjusted, when the vehicle is parked, or, alternatively, is marshalling,i.e. when the vehicle is conducted at a speed below about 10 to 20 km/h.When the vehicle is parked or being marshalled, the elevation may beadjusted between the lowest level 20 a and the highest level 20 b. Thedistance between these two levels is typically about 30 cm. This meansthat the loading platform may be adjusted between an elevation of about75 cm above ground level and an elevation of about 105 cm above groundlevel.

When the control unit has assumed its driving mode. i.e. preferably whenthe vehicle is operated in the driving mode, i.e. when the vehicle isnot parked, or is driven at a speed exceeding about 20 km/h, theelevation is adjustable between a lowest level 21 a and a highest level21 b. The distance between these two levels is typically about 10 cm.This means that the loading platform may be adjusted between anelevation of about 80 cm above ground level and in elevation of about 90cm above ground level.

FIG. 7 shows a control unit 90 for operation and adjustment of thedistance between wheel axle and frame structure. The control unitcomprises means for adjustment of the size of the distance, and selectormeans for switching the control unit 80 into a driving mode or aparking/marshalling mode. The control unit 90 comprises a first switch91, a second switch 92, a third switch 93, and a fourth switch 94.

The first switch can be switched between a first position 95, a secondposition 96, and a third position 97. When the switch is set to itsfirst position 95, the elevation of the LCV loading platform isadjustable within the first larger range, 20 a and 20 b. Thiscorresponds to the control unit being set to its parking or marshallingmode. When the switch is set to its second position 96, the control unitwill assume its driving mode, and the vehicle will assume its presetride height of the loading platform and the frame structure. When theswitch is set to its third position 97, the ride height is adjustablewithin the second, smaller range, 21 a and 21 b.

The third switch 93 can be switched between a first position 98, asecond position 99, and a neutral position. When the third switch 93 isset to its first position 98, the desired elevation is increased. Whenthe third switch 93 is set to its second position 99, the desiredelevation is decreased. When the third switch 93 is set to its neutralposition, the first and the second valve means will assume suchpositions as to allow neither compressed air into or out from thepneumatic suspension means. This means that the first, the third and thefourth solenoid valves, 50, 52 and 69, are all set to their respectivesecond positions, 50 b, 52 b and 71 b.

The elevation adjustment, i.e. the setting of the desired height levelof the loading platform, and of the size of the desired distance betweenthe wheel axle and the frame structure, respectively, within the smallerrange, when the control unit is set into its driving mode, as well asthe larger range when the control unit is set into its parking ormarshalling mode, is made by pushing the third switch from its neutralposition to either its first position, thereby increasing the setelevation, or to its second position, thereby reducing the setelevation. When the elevation is increased, the second valve means isset to such a mode as to connect the compressed air supply to the mainline 59. This means that the second solenoid valve 51 is set to itsfirst position 51 a. When the elevation is decreased, the second valvemeans is set to such a mode as to connect the main line 59 to the drainline. This means that the second solenoid valve 51 is set to its secondposition 51 b.

The fourth switch 94 is used to change the control unit switches intoother function modes, such as in order to allow resetting of thedefault, factory set ride height, to retrieve and program a number ofpreselected elevations when the control unit is set to its parking ormarshalling mode.

The second switch 92 may selectively be set into a first position 102, asecond position 103, or a third position 104.

When the second switch 92 is set to its first position 102, the firstvalve means 48, and the second valve means 68 are set in such a manneras to affect only the elevation setting of the front axle. This meansthat the first and the third solenoid valves, 50 and 52, are set totheir respective second positions, 50 b and 52 b, whereas the fourthsolenoid valve 69 is set to its first position 71 a.

When the second switch 92 is set to its second position 103, the firstvalve means 48, and the second valve means 68 are set in such a manneras to affect the elevation adjustment of the front axle and the rearaxle, or rear axles, simultaneously. This means that the first and thethird solenoid valves, 50 and 52, are set to their respective firstpositions, 50 a and 52 a, and the fourth solenoid valve 69 is set to itsfirst position 71 a.

When the second switch 92 is set to its third position 104, the firstvalve means 48, and the second valve means 68 are set in such a manneras to affect only the elevation setting of the rear axle or axles. Thismeans that the first and the third solenoid valves, 50 and 52, are setto their respective first positions, 50 a and 52 a, whereas the fourthsolenoid valve 69 is set to its second position 71 b.

The control unit 90 is in signalling connection with the control unit80. The control unit 90 is detachably arranged in the cab 3 in order toallow for the control unit to be positioned inside or outside the cab 3.

The elevation adjustment is preferably performed when the vehicle isparked. Setting of the control device to a driving mode does not meanthat the vehicle is operated in a driving mode at present. Setting thecontrol device to a driving mode means that the elevation adjustment canbe made within the range appropriate for operating the vehicle in adriving mode.

The reference “LCV” shall mean a trailer as well as a tractor vehicle.

The reference “ride height” shall mean the elevation above ground levelthat the loading platform of an LCV has assumed when the control unit isset to a driving mode.

The reference “marshalling” shall mean that the vehicle is driven at lowspeed.

The reference “operated in a driving mode” shall mean that the vehicleis driven at a speed exceeding a certain limit speed.

Although the invention herein has been described with reference toparticular embodiments, it is to be understood that these embodimentsare merely illustrative of the principles and applications of thepresent invention. It is therefore to be understood that numerousmodifications may be made to the illustrative embodiments and that otherarrangements may be devised S without departing from the spirit andscope of the present invention as defined by the appended claims.

What is claimed is:
 1. Apparatus for adjusting the height of a vehicleframe on a vehicle including a vehicle suspension system, said apparatuscomprising vehicle frame elevation adjustment means for adjusting theelevation of said vehicle frame, and control means for controlling saidvehicle frame elevation adjustment means, said control means adapted tobe set in a first mode corresponding to normal driving of said vehicleand a second mode corresponding to parking or marshalling of saidvehicle, whereby when said control means is in said first mode saidvehicle frame elevation adjustment means permits adjustment of saidvehicle frame within a first range and when said control means is insaid second mode said vehicle frame elevation adjustment means permitsadjustment of said vehicle frame within a second range, said first rangebeing greater than said second range, and said second range being withinsaid first range.
 2. The apparatus of claim 1 wherein said vehicle frameelevation adjustment means comprises a pneumatic suspension system forsaid vehicle.
 3. The apparatus of claim 2 wherein said vehicle includesat least one wheel axle, and said vehicle frame elevation adjustmentmeans adjusts said elevation of said vehicle frame with respect to saidat least one wheel axle.
 4. The apparatus of claim 3 wherein saidpneumatic suspension system is arranged between said vehicle frame andsaid at least one wheel axle, said control means including selectormeans for selecting one of said first and second modes, and saidpneumatic suspension system including a source of compressed air, valvemeans for controllably feeding said compressed air to said pneumaticsuspension system or draining said compressed air from said pneumaticsuspension system in response to said control means, whereby saidpneumatic suspension system is expanded or compressed in order to adjustthe distance between said vehicle frame and said at least one wheelaxle, said distance between said vehicle frame and said at least onewheel axle being adjusted within said first range when said controlmeans is in said first mode and within said second range when saidcontrol means is in said second mode.
 5. The apparatus of claim 4including measuring means for measuring the distance between saidvehicle frame and said at least one wheel axle.
 6. The apparatus ofclaim 4 wherein said measuring means comprises an angular positionsensor, a lever connected to said angular position sensor, and a controlrod articulated with respect to said lever, said angular position sensorbeing attached to one of said vehicle frame and said at least one wheelaxle and said control rod being attached to the other of said vehicleframe and said at least one wheel axle, whereby said angular positionsensor measures the angular position of said lever so that when saiddistance between said vehicle frame and said at least one wheel axle isaltered by means of said pneumatic suspension system the position ofsaid control rod is altered, thereby altering the angular position ofsaid lever sensed by said angular position sensor, said control meansincluding means for reading said angular position of said lever anddetermining the distance between said vehicle frame and said at leastone wheel axle based thereon.
 7. The apparatus of claim 6 wherein saidpneumatic suspension system includes air bellows comprising a flexiblematerial, a base for said air bellows, and a top for said air bellows,said air bellows, said base and said top defining a closed space, andconnection means connecting said valve means with said closed space,said pneumatic suspension system including a cylindrical surface,whereby said bellows is adapted to roll onto said cylindrical surfacewhen said pneumatic suspension system is compressed and to roll off ofsaid cylindrical surface when said pneumatic suspension system isextended.
 8. The apparatus of claim 7 wherein said cylindrical surfaceis incorporated in said base, and said base is attached to said at leastone wheel axle.
 9. The apparatus of claim 8 wherein said cylindricalsurface comprises a hollow body, whereby the volume of said closed spaceis increased.
 10. The apparatus of claim 2 wherein the limits of saidfirst range are defined by the maximum extension and compression of saidpneumatic suspension system.
 11. The apparatus of claim 1 includingselector means connected to said control means, said selector meansbeing manually settable between said first mode and said second mode.12. The apparatus of claim 1, wherein said normal driving of saidvehicle corresponds to driving said vehicle at a speed greater thanabout 20 km/h, said marshalling of said vehicle corresponds to drivingsaid vehicle at a speed below about 20 km/h, and said parking of saidvehicle corresponds to said vehicle at 0 km/h.
 13. Apparatus foradjusting the distance between a vehicle frame and at least one wheelaxle of a vehicle having a suspension system, said apparatus comprisinga control unit including control members for setting a desired value forsaid distance, control means adapted to be set in a first mode and asecond mode, and selector means for selecting one of said first andsecond modes for said control means whereby when said control means isin said first mode said desired value for said distance is within afirst range and when said control means is in said second mode saiddesired value for said distance is within a second range, said firstrange being greater than said second range, and said second range beingwithin said first range.
 14. The apparatus of claim 13 wherein saidvehicle includes a cab and wherein said control means is attachablymounted in said cab.
 15. The apparatus of claim 13 wherein said firstmode corresponds to normal driving of said vehicle and said second modecorresponds to parking or marshalling of said vehicle.
 16. The apparatusof claim 13 wherein said selector means comprises a manual switch.